The art of fabricating containers and vessels has its roots in antiquity. In modern times, containers and vessels of all types, shapes, and sizes, are fabricated to meet the needs of a rapidly expanding world economy. The present invention is concerned with the manufacture of light weight canisters, capable of storing materials under a pressure of at least approximately 300 psi.
The typical method of fabricating pressure-type canisters is to weld a pair of distally placed closure elements, or end caps, to a metal shell body. Light weight, aluminum canister tube bodies, however, are not conducive to welding. Aluminum welding must be performed in an expensive, inert atmosphere of argon to prevent an oxide coat from forming and interfering with the weld process. More importantly, aluminum tends to anneal and weaken when subjected to welding temperatures, thus necessitating a thicker shell body. The thicker shell adds weight and cost to the finished product, and defeats the light weight objective. The thicker tube shell has the further disadvantage of reducing the amount of material that can be stored in the canister.
The current invention is for a light weight aluminum canister that forms a mechanical seal with its end caps by the method of electromagnetic forming. Electromagnetic forming is a well known process, wherein an electric coil is placed around a metal body, and is thereafter electrically pulsed to create a magnetic field that shapes the metal. In the present application, coils are placed about the distal ends of the shell tube. The coil is then electrified with a high energy voltage pulse of short duration, which magnetically forms and mechanically seals the shell body about the end caps. A typical electromagnetic forming process is described in U.S. Pat. No. 3,837,755, issued to BENOIT et al on Sep. 24, 1974, entitled "Multi-Piece Rod for Control and Structural Members"; and U.S. Pat. No. 4,523,872, issued to ARENA et al on Jun. 18, 1995, entitled "Torsion Resistant Grooved Joint".
The end caps used in the pressure canister of this invention can be formed from a variety of metallic or non-metallic materials. In the preferred embodiment of the inventive canister, the end cap material is a plastic material. A suitable plastic that has been chosen with the required attributes light weight, of strength and ductility is DELRIN.RTM.. DELRIN.RTM. is an injection moldable thermoplastic, fabricated from an acetal resin. It can be injection molded with reinforcing fibers to provide greater strength and ductility.